1. Field of the Invention;
The present invention relates to a method of adding an organic silane compound on a surface of an organic polymer membrane by a photochemical reaction to silylate the surface of said polymer membrane, and to a method of forming a fine pattern accurately on a substrate for a variety of semiconductors or semiconductor devices.
2. Related Art Statement;
One of the conventional methods for adding an organic metal compound selectively on a surface of a polymer membrane is a selective chemical vapor deposition method (CVD method) of tetrachlorosilane gas. This known method is based on the principle that organic silane compounds have little tendency to be deposited on the surface of a perfluoro hydrocarbon polymer having a small surface energy to achieve the aimed selectivity. It is thus necessary to use a special polymer material in order to achieve satisfactory selectivity. However, it is difficult to achieve satisfactory selectivity with good reproducibility, since the selectivity is seriously affected by the deposition conditions the organic silane compound. The organic silane layer formed by this known method is deposited physically on the surface of the polymer rather than being coupled by chemical bonds.
The bi-layer resist systems and tri-layer resist systems have been developed to form an extremely fine pattern accurately.
Different from the resist coating applied by the conventional system wherein a single resist membrane is used to form a pattern, the resist coating formed through the bi-layer or tri-layer system has an advantageous effect that the local fluctuation is thickness, which often poses adverse affection on the formation of pattern, is eliminated. A further advantage of the bi-layer or tri-layer system resides in that the top resist layer forming the image can be thinner than that in the single layer system to form a fine pattern with accuracy. However, these known systems include complicated processing steps and require special resist materials.
In the tri-layer resist system, an organic polymer layer is coated on a substrate and baked, and then an inorganic polysilicon or SiO.sub.2 or a silicon containing resin is applied on the baked organic polymer layer to form a middle layer on which a resist layer is coated to prepare the triple layer structure. A pattern is formed by the top resist layer through the conventional lithography, and the inorganic or silicon containing resin layer is etched in a Freon gas plasma while utilizing the pattern formed by the top resist layer as the masking. As a result of etching, the regions of the middle layer covered by the top resist pattern is left unetched. Then the organic polymer layer, i.e. the bottom layer, is subjected to dry etching in an oxygen gas plasma through the masking pattern formed by the unetched middle layer. The top resist pattern is removed during the dry etching step, since it is not durable to the oxygen gas plasma to leave the pattern covered by the middle layer. In this process, the middle layer made of an inorganic material or a silicon containing resin having the oxygen plasma durability must be applied to form a mask, since it is difficult to etch the bottom organic polymer layer directly while using the top polymer pattern as a mask durable to dry etching.
In contrast thereto, the bi-layer resist system is characterized by the use of a top resist layer which is durable to oxygen plasma. If such a resist material that is durable to oxygen plasma is developed, a pattern is formed by the top resist material directly on the bottom organic polymer layer, without the need of providing the middle inorganic layer, to be ready for processing through the dry etching.
In order to provide an organic resist material having the oxygen plasma durability, it has already been proposed to introduce Si-containing groups in the main or side chain of the polymer by copolymerization, graft polymerization or esterification, to prepare an Si-containing resist material. For example, U.S. Pat. No. 4,507,384 discloses a siloxane polymer-containing resist material for forming a pattern. The resist material proposed by this prior Patent is prepared by introducing chloromethyl groups into the phenyl groups of a polyphenylsiloxane, and then substituting the chloro groups of the chloromethyl groups by acryloyloxy-, methacryloyloxy- or cinnamoyloxy-groups. It is generally known that silicon contained in a polymer as a structural element affects significant influences on the basic properties thereof, when the polymer is used as a resist forming material, including the solubility in a solvent sensitivity and the resolution. Due to the adverse affections on the basic properties induced by the introduction of silicon, it has been difficult to provide a polymer with the oxygen plasma durability without deteriorating the basic properties thereof for forming satisfactory resist pattern. For this reason, all of the known resist materials for forming negative and positive images by the irradiation of ultraviolet rays and the known resist materials for forming negative images could not be deemed as having totally satisfactory performance characteristics. The quality of a pattern formed by the bi-layer resist system depends principally on the quality of the pattern forming top resist layer and the oxygen plasma durability thereof. The bi-layer resist system has not yet been used for practical applications, due to the fact that an Si-containing resist material excellent in total performance characteristics has not been developed.
U.S. Pat. No. 4,551,418 discloses a method of forming a resist pattern of a negative image by a cationic photo polymerization. The method disclosed by the prior Patent comprises the steps of coating a polymer layer containing a cationic photo polymerization initiator, treating the thus coated polymer layer with a cationically sensitive organic silicone monomer, irradiating the thus treated organic layer with a deep ultraviolet ray to form a pattern which is durable to plasma etching, and then subjecting the polymer layer to plasma etching to leave the pattern protected by the durable resist. The principle utilized in this method is that selected portions of p-tert-butoxycarbonyloxystyrene selected specifically as a polymer having a photosensitivity to a deep ultraviolet ray are exposed to a deep ultraviolet ray so that the portions exposed to the deep ultraviolet ray are selectively silylated by the subsequent step of allowing the polymer to contact with a hexamethylsilazane solution and the subsequent thermal treatment to form a pattern. Since the pattern is formed by silylating the exposed portions of the polymer, with the unexposed portions being not silylated, in this known method, satisfactory selectivity for forming a clear image can be scarcely attained for the principal defect involved therein. The method is detrimental in that the edge definition of the pattern is inferior, and that the etching rate ratio to the oxygen RIE cannot be set to a sufficiently high level, leading to the disadvantage that difficulties are encountered in forming a fine pattern with high accuracy. The resist material usable in this method is limited only to the aforementioned polymer, and the light which may be used in the lithographical pattern forming step is limited to deep ultraviolet rays. This prior Patent fails to teach the provision of laminated organic polymer membrane comprised of an active organic polymer which is reactive with an organic silane compound under the irradiation of a deep ultraviolet ray to be coupled with the silyl groups at the surface of the polymer, and an inert organic polymer which is not reactive with the organic silane compound; and also fails to teach a method of forming a pattern by ordinary lithographic technique using the organic polymer membrane, and a method of silylating selective portions of the surface of the active polymer.